This week I level the floor using a self leveling underlayment. I have never done this before and it turned out great so any DIY beginner can accomplish this project with ease. It is very easy and actually quite fun and satisfying!
Primer: https://amzn.to/3xzgVPP
Self Leveling Underlayment: https://www.homedepot.com/p/Henry-555-Level-Pro-40-lb-Self-Leveling-Underlayment-12165/100549588
Great Stuff Foam: https://amzn.to/3mV85qN
Silicone: https://amzn.to/3mZtcYQ